The invention relates to an apparatus for changing the onset of fuel injection within a fuel injection pump intended to supply internal combusion engines. The fuel injection pump to which this invention relates is supplied with a rotating shaft equipped with flyweights that move under a centrifugal force and are returned by a return spring. The position of the flyweights determines the relative rotational position of a driven and a driving shaft.
The prevailing and increasingly rigorous regulations regarding environmental contamination, i.e., exhaust gas regulations, make it imperative that the onset of injection, i.e., the timing of the injection of fuel by a fuel injection pump, be made dependent not only on the engine rpm but also on other operational variables, for example the injected fuel quantity, i.e., the load on the engine. Thus, the power as well as the exhaust gas conditions could be considered in the operation of the engine. When the engine is heavily loaded and the combustion temperature rises, the injection onset must be retarded or moved back so as to limit the concentration of NO.sub.x components in the exhaust gases and to thereby lower the combustion temperature. It is known to provide this requirement by an apparatus disclosed in the Japanese Pat. No. 47-40228 and the laid-open patent application No. 47-23720 which describe control systems that employ electrical and other means to obtain a correction of the onset point for fuel injection on the basis of engine rpm and of engine load. However, the electrical circuits and the hydraulic actuating members described in these publications are very complicate and expensive and require substantial amounts of space.